1. Field of the Invention
The present invention relates to selected propellant formulations based on energetic oxetane binder systems exhibiting low, zero or negative pressure exponents across a pressure region, e.g., plateau ballistic behavior.
2. Background Information
Solid propellants are used extensively in the aerospace industry. Solid propellants have developed as the preferred method of powering most missiles and rockets for military, commercial, and space applications. Solid rocket motor propellants have become widely accepted because of the fact that the propellants are relatively simple to formulate and use and have excellent performance characteristics. Furthermore, solid propellant rocket motors are generally very simple when compared to liquid fuel rocket motors. For all of these reasons, it is found that solid rocket propellants are often preferred over other alternatives, such as liquid propellant rocket motors.
Typical solid rocket motor propellants are generally formulated having an oxidizing agent, a fuel, and a binder. At times, the binder and the fuel may be the same. In addition to the basic components set forth above, it is conventional to add various plasticizers, curing agents, cure catalysts, and other similar materials which aid in the processing and curing of the propellant. A significant body of technology has developed related solely to the processing and curing of solid propellants, and this technology is well known to those skilled in the art.
One type of propellant that is widely used incorporates ammonium perchlorate ("AP") as the oxidizer. The AP oxidizer may then, for example, be incorporated into a propellant which is bound together by a hydroxy-terminated polybutadiene (HTPB) binder. These HTPB binders are widely used and commercially available. It has been found that such propellant compositions provide ease in manufacting and handling; exhibit good performance characteristics; and are at the same time economical and reliable. In essence, it can be said that AP composite propellants have been the backbone of the solid propulsion industry for approximately the past 40 years.
One of the problems encountered in the design of rocket motors is the control of the thrust output of the rocket motor. This is particularly true when it is desired to operate the motor in two or more different operational modes. For example, it is often necessary to provide a high level of launch-phase thrust in order to "boost" the motor and its attached payload from a starting position, such as during launch of a rocket or missile. Once the launch phase has been completed, it may be desirable to provide a constant output from the rocket motor over an extended "sustain" operation. This sustain may occur, for example, after the rocket has been placed in flight and while it is traveling to its intended destination.
The achievement of such multi-phased or biplateau operations has been extremely difficult. It has been necessary to resort to complex mechanical arrangements in the rocket motors. Alternatively, less efficient and less desirable liquid rocket motors have been used to obtain multi-phase operation.
In some cases, multiple-phase or biplateau operation has been attempted by constructing very complex propellant grains, such as grains having multiple propellants. In any case, achievement of multiple-phase operation has been complex, time consuming, and costly.
Single plateau propellant offers reduced temperature sensitivity, allows high pressure operation, and a higher expansion ratio for increased performance without affecting motor safety margins. Plateau propellant in general reduces margins required between the maximum expected operating pressure (MEOP) and the maximum nominal pressure. This in turn reduces motor case inert weight and makes high pressure motor operations advantageous.
Still further efforts have focused on non-energetic binder systems in an effort to develop plateau propellants. While offering some advantages, the art is still seeking IM propellants having a higher delivered impulse at lower solids loadings.